The present invention relates to a color copier, color printer or similar image recording apparatus and, more particularly, to an image recording apparatus of the type having an image carrier, and an intermediate transfer belt passed over rollers and provided with guides to be prevented from deviating in position. In this type of apparatus, toner images of respective colors are sequentially formed on the image carrier and then transferred to the belt, which is rotated in a reciprocating motion, and the resulting composite toner image is transferred from the belt to a paper or similar recording medium.
In the above-described type of image recording apparatus, the intermediate transfer belt is generally rotated in opposite directions in a reciprocating motion, as mentioned above, or only in the forward direction for the transfer of the toner images from the image carrier to the belt. The forward rotation scheme is such that after the transfer of a toner image of first color to the belt, the belt is continuously rotated in the forward direction, a toner image of second color is transferred to belt with the leading edge thereof in register with that of the toner image of first color, and then toner images of third and fourth colors are sequentially transferred to the belt in the same manner. On the other hand, the reciprocation scheme is such that after the transfer of the toner image of first color to the belt, the belt is returned by the same distance as it moved in the forward direction (during the return, the belt is spaced apart from the image carrier), the toner image of second color is transferred to the belt with the leading edge thereof in register with that of the toner image of first color, and then toner images of third and fourth colors are sequentially transferred to the belt in the same manner.
Considering changes in the circumferential length of the belt, the reciprocation scheme, which returns the belt the same distance by use of a stepping motor or similar drive source, is advantageous over the forward rotation scheme. It has been reported that the belt deviates to either side due to, among others, the degree of parallelism of rollers over which it is passed, and that the deviation during forward movement and the deviation during reverse movement are opposite in direction. It follows that the deviations during forward movement and reverse movement are substantially equal to each other. Therefore, the individual toner images combined on the belt appear almost in accurate register.
However, assume an image recording apparatus having an intermediate transfer belt which is provided with guides at opposite edges thereof in order to be prevented from deviating to either side while in rotation. The problem with this kind of apparatus is that when the belt is continuously rotated in one direction, it is prevented from deviating more than a predetermined amount by the guides. When the reciprocation scheme is applied to such a belt, the belt does not deviate during the formation of a toner image of first color, i.e., while in forward rotation, due to the guides. However, in the event of reverse rotation, the belt deviates in the opposite direction noticeably. This is also true with the formation of toner images of second, third and fourth colors although the degree of deviation is reduced. As a result, the consecutive deviations are summed up to result in a substantial total deviation. Experiments showed that the total deviation of the belt ranges from 0.3 mm to 1 min.